Stability control system

ABSTRACT

Embodiments of a suspension for a vehicle is provided. The suspension includes, for example, a frame and a locking assembly. The locking assembly inhibits tipping of a frame of the vehicle when tipping of the frame is detected.

RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.15/146,260, filed on May 4, 2016 and titled “STABILITY CONTROL SYSTEM,”now U.S. Pat. No. 9,827,823, which is a divisional application of U.S.Ser. No. 14/566,899, filed on Dec. 11, 2014 and titled “STABILITYCONTROL SYSTEM,” now U.S. Pat. No. 9,346,335, which is a divisionalapplication of U.S. Ser. No. 12/524,476, filed on Jul. 24, 2009 andtitled “WHEELCHAIR WITH SUSPENSION” now U.S. Pat. No. 8,910,975, whichis the U.S. National Stage Entry of PCT/US2008/053242, filed on Feb. 7,2008, which claims the benefit of U.S. Provisional Patent ApplicationSer. No. 60/901,513, filed on Feb. 14, 2007 and titled “STABILITYCONTROL SYSTEM,” the entire disclosures of which are fully incorporatedherein by reference.

BACKGROUND

Wheelchairs and scooters are an important means of transportation for asignificant portion of society. Whether manual or powered, thesevehicles provide an important degree of independence for those theyassist. However, this degree of independence can be limited if thewheelchair is required to traverse obstacles such as, for example, curbsthat are commonly present at sidewalks, driveways, and other pavedsurface interfaces. This degree of independence can also be limited ifthe vehicle is required to ascend inclines or descend declines.

Most wheelchairs have front and rear casters to stabilize the chair fromtipping forward or backward and to ensure that the drive wheels arealways in contact with the ground. The caster wheels are typically muchsmaller than the driving wheels and located both forward and rearward ofthe drive wheels. Though this configuration provides the wheelchair withgreater stability, it can hamper the wheelchair's ability to climb overobstacles such as, for example, curbs or the like, because the size ofthe front casters limits the height of the obstacle that can betraversed.

Though equipped with front and rear suspended casters, most mid-wheeldrive wheelchairs exhibit various degrees of tipping forward or rearwardwhen descending declines or ascending inclines. This is because thesuspensions suspending the front or rear stabilizing casters arecompromised so that they are not made too rigid, which would preventtipping and also not provide much suspension, or are made too flexiblethereby effectively not providing any degree of suspension orstabilization.

SUMMARY

According to one embodiment, a suspension for a vehicle is provided. Thesuspension includes, for example, a stabilizing assembly. Thestabilizing assembly inhibits tipping of a frame of the vehicle whentipping of the frame is detected.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which are incorporated in and constitute apart of the specification, embodiments of tip or stability controlsystems, sub-assemblies, and components are illustrated, which togetherwith a general description given above and the detailed descriptiongiven below, serve to explain the principles of tip or stability controlsystems, sub-assemblies and components.

FIG. 1A is an illustration of a rear of an embodiment of a mid-wheeldrive wheelchair;

FIG. 1B is a view taken along lines 1B-1B in FIG. 1A, illustrating aside of the mid-wheel drive wheelchair;

FIG. 1C is a view taken along lines 1C-1C in FIG. 1B, illustrating afront of the mid-wheel drive wheelchair;

FIG. 2 is a flow chart that illustrates an embodiment of a method ofcontrolling tipping of a mid-wheel drive wheelchair frame;

FIGS. 3A-3C illustrate the wheelchair of FIGS. 1A-1C, where one rearcaster has moved downward relative to a frame;

FIGS. 4A-4C illustrate the wheelchair of FIGS. 1A-1C, where thewheelchair is exhibiting a tipping behavior;

FIG. 5 is an illustration of an embodiment of a wheelchair with a fluidcylinder stabilizing assembly;

FIG. 6 is an illustration of an embodiment of a wheelchair with a fluidcylinder with spring return stabilizing assembly;

FIGS. 7A-7C illustrate an embodiment of a mid-wheel drive wheelchairthat is similar to the wheelchair shown in FIGS. 1A-1C where twostabilizing members are linked;

FIGS. 8A-8C illustrate an embodiment of a mid-wheel drive wheelchairthat is similar to the wheelchair shown in FIGS. 1A-1C that includes asingle stabilizing member or assembly;

FIGS. 9A-9C illustrate an embodiment of a mid-wheel drive wheelchairthat is similar to the wheelchair shown in FIGS. 1A-1C where twotriggers or sensors are linked;

FIGS. 10A-10C illustrate an embodiment of a mid-wheel drive wheelchairthat is similar to the wheelchair shown in FIGS. 1A-1C that includes asingle trigger or sensor;

FIGS. 11A-11C illustrate an embodiment of a mid-wheel drive wheelchairthat is similar to the wheelchair shown in FIGS. 1A-1C that includes arear caster position sensing linkage coupled to a single trigger orsensor that indicates when both rear casters drop relative to a frame;

FIGS. 12A-12C illustrate the wheelchair of FIGS. 11A-11C, where one rearcaster has moved downward relative to a frame;

FIGS. 13A-13C illustrate the wheelchair of FIGS. 11A-11C, where thewheelchair is exhibiting a tipping behavior;

FIGS. 14A-14C illustrate an embodiment of a mid-wheel drive wheelchairthat is similar to the wheelchair shown in FIGS. 1A-1C that includes arear caster position sensing linkage coupled to a pair of triggers orsensor that indicates when both rear casters drop relative to a frame;

FIGS. 15A-15C illustrate the wheelchair of FIGS. 14A-14C, where one rearcaster has moved downward relative to a frame;

FIGS. 16A-16C illustrate the wheelchair of FIGS. 14A-14C, where thewheelchair is exhibiting a tipping behavior;

FIG. 17A illustrates a rear view of an embodiment of a rear castersuspension with a rear caster position sensing arrangement;

FIG. 17B is a view taken along lines 17B-17B in FIG. 17A, illustrating aside view of the rear caster suspension and rear caster position sensingarrangement;

FIG. 17C is a view taken along lines 17C-17C in FIG. 17A, illustrating atop view of the rear caster suspension and rear caster position sensingarrangement;

FIGS. 18A and 18B illustrate the rear caster suspension and rear casterposition sensing arrangement of FIGS. 17A-17C, where one rear caster hasmoved downward;

FIGS. 19A and 19B illustrate the rear caster suspension and rear casterposition sensing arrangement of FIGS. 17A-17C, where both rear castershave moved downward;

FIGS. 20A-20C illustrate an embodiment of a rear caster suspension andrear caster position sensing arrangement that is similar to the rearcaster suspension and rear caster position sensing arrangement shown inFIGS. 17A-17C where movement of a first rear caster pivot arm depends ona position of a second rear caster pivot arm;

FIGS. 21A and 21B illustrate the rear caster suspension and rear casterposition sensing arrangement of FIGS. 20A-20C, where one rear caster hasmoved downward;

FIGS. 22A and 22B illustrate the rear caster suspension and rear casterposition sensing arrangement of FIGS. 20A-20C, where further downwardmovement of one rear caster is inhibited by a second rear caster;

FIG. 23A illustrates a rear of an embodiment of a rear caster suspensionand rear caster position sensing arrangement;

FIG. 23B is a view taken along lines 23B-23B in FIG. 23A, illustrating aside of the rear caster suspension and rear caster position sensingarrangement;

FIG. 23C is a view taken along lines 23C-23C in FIG. 23A, illustrating atop of the rear caster suspension and rear caster position sensingarrangement;

FIGS. 24A-24C illustrate the rear caster suspension and rear casterposition sensing arrangement of FIGS. 23A-23C, where downward movementof one rear caster is inhibited by a second rear caster;

FIGS. 25A-25C illustrate an embodiment of a rear caster suspension andrear caster position sensing arrangement that is similar to the rearcaster suspension and rear caster position sensing arrangement of FIGS.23A-23C, where the rear casters are connected to a pivotable arm;

FIG. 26 illustrates an embodiment of a mid-wheel drive wheelchair thatincludes a tip or stability control system and front caster pivot armthat are coupled to drive assemblies;

FIG. 27 illustrates an embodiment of a mid-wheel drive wheelchair thatincludes a tip or stability control system and front caster pivot armsthat are coupled to drive assemblies;

FIG. 28 illustrates an embodiment of a mid-wheel drive wheelchair thatincludes a tip or stability control system and front caster pivot armsthat are coupled to drive assemblies;

FIG. 29 illustrates an embodiment of a mid-wheel drive wheelchair thatincludes a tip or stability control system and front caster pivot armsthat are coupled to drive assemblies;

FIG. 30 illustrates an embodiment of a mid-wheel drive wheelchair thatincludes a tip or stability control system and front caster pivot armsthat are coupled to drive assemblies;

FIG. 31 illustrates an embodiment of a mid-wheel drive wheelchair thatincludes a tip or stability control system and front caster pivot armsthat are coupled to drive assemblies;

FIG. 32 is a perspective view of an embodiment of a mid-wheel drivewheelchair that includes a tip or stability control system;

FIG. 33 is a side view of the mid-wheel drive wheelchair of FIG. 32;

FIG. 34 is a view taken along lines 34-34 in FIG. 33;

FIG. 35 is a view taken along lines 35-35 in FIG. 33;

FIG. 36 is a view taken along lines 36-33 in FIG. 33;

FIG. 37 is a view taken along lines 37-37 in FIG. 33;

FIG. 38 is a view of the wheelchair of FIG. 32 with components removed;

FIG. 39 is a side view of the mid-wheel drive wheelchair with componentsremoved of FIG. 38;

FIG. 40 is a view taken along lines 40-40 in FIG. 39;

FIG. 41 is a view taken along lines 41-41 in FIG. 40;

FIG. 42 is an enlarged portion of FIG. 38 as indicated by reference FIG.42 in FIG. 38;

FIG. 43 is a schematic illustration of a vibration damping assembly;

FIG. 44 illustrates a perspective view of a rear caster position sensingarrangement and rear caster suspension of the wheelchair illustrated byFIG. 32;

FIG. 45 is a side view of the rear caster position sensing arrangementand rear caster suspension of FIG. 44;

FIG. 46 is a view taken along lines 46-46 in FIG. 45;

FIG. 47 is a view taken along lines 47-47 in FIG. 45;

FIG. 48 is a view taken along lines 48-48 in FIG. 46;

FIG. 49 is a view taken along lines 49-49 in FIG. 48;

FIG. 49A is a view similar to FIG. 49, where the rear caster positionsensing arrangement has moved to an engaged position; and

FIG. 50 is a view taken along lines 50-50 in FIG. 45.

DETAILED DESCRIPTION

The present description provides multiple embodiments of suspensionsystems for vehicles, such as, wheelchairs, including, but not limitedto mid-wheel drive wheelchairs, scooters, and other personal mobilityvehicles. The drawings illustrate the suspension systems on mid-wheeldrive wheelchairs. However, the described suspensions can be implementedon any personal mobility vehicle, including scooters and rear drivewheelchairs.

The suspension systems include a tip or stability control system.Generally, the control system includes a trigger or sensor for sensingwhen conditions exist that may cause the vehicle to exhibit a tippingbehavior, which can be either forward or rearward, and a stabilizingmember or assembly that stabilizes the suspension system to prevent anyfurther tipping behavior. The trigger or sensor also senses when thevehicle is no longer subject to conditions that may cause it to exhibita tipping behavior and causes the stabilizing member or assembly to nolonger inhibit movement of the suspension system. A variety of differentcontrol system features are disclosed in the context of the followingexemplary embodiments. The individual features of the followingembodiments may be used alone or in combination with features of otherembodiments.

One feature of some control system embodiments disclosed herein is thatupward movement of one front caster is inhibited to prevent tipping onlyif upward movement of the other front caster is also inhibited. Anotherfeature of some control system embodiments disclosed herein is that therelative positions of two rear casters are sensed to determine a tippingbehavior. For example, a tipping behavior may be indicated only whenboth rear casters move downward relative to a frame.

FIGS. 1A, 1B, and 1C schematically illustrate a mid-wheel drivewheelchair 100 that includes a tip or stability control system thatcomprises one or more sensors 112 and one or more stabilizing members orassemblies 114. The control system 100 can also be applied to a widevariety of other vehicles, including but not limited to, rear drivewheel chairs, front drive wheel chairs, scooters, and other personalmobility vehicles. The wheelchair 100 includes a frame 102, a seat 104supported by the frame, first and second drive wheels 106 that supportthe frame, first and second front casters 108 a, 108 b, first and secondrear casters 110 a, 110 b, one or more sensors 112, and one or morestabilizing members or assemblies 114. In this application, the term“frame” refers to any component or combination of components that areconfigured for mounting of a drive assembly and a caster pivot arm. Thefirst and second front casters 108 a, 108 b are coupled to the frame 102such that the front casters are moveable upwardly and downwardly withrespect to the frame as indicated by double arrow 116. In the exampleillustrated by FIGS. 1A, 1B, and 1C, the front casters are independentlycoupled to the frame 102 by separate pivot arms 118 a, 118 b. In anotherembodiment, the pivot arms 118 a, 118 b are coupled such that movementof one pivot arm is transferred to the other pivot arm. For example, atorsion bar (not shown) may couple the pivot arms 108 a, 108 b. Thefirst and second rear casters 110 a, 110 b are coupled to the frame 102such that the rear casters are moveable upwardly and downwardly withrespect to the frame. In the example illustrated by FIGS. 1A, 1B, and1C, the rear casters are independently coupled to the frame 102 byseparate rear caster pivot arms 120 a, 120 b. In another embodiment, therear caster pivot arms 120 a, 120 b are coupled such that movement ofone pivot arm is transferred to the other pivot arm (See the embodimentof FIG. 23 for example).

One stabilizing member 114 is coupled to each front caster pivot arms118 a, 118 b and to the frame 102. However, any number of stabilizingmembers 114 can be used, may take any form, and may be coupled to thefront caster pivot arm and the frame in any manner that allows thestabilizing member or members to inhibit movement of one or more of thefront caster pivot arms with respect to the frame in at least onedirection. Examples of stabilizing members that may be used include, butare not limited to, the stabilizing members disclosed herein and thelocking members disclosed in U.S. Pat. No. 6,851,711 to Goertzen et al,United States Patent Application Publication No. 2004/0150204, andUnited States Patent Application Publication No. 2005/0151360 toBertrand et al., which are all incorporated herein by reference in theirentireties.

One trigger or sensor 112 is coupled to each of the rear caster pivotarms 120 a,b in the example illustrated by FIGS. 1A, 1B, and 1C.However, any number of triggers or sensors 112 can be used, may take anyform and may be positioned in any way that allows tipping of the frame102 to be sensed. Examples of triggers or sensors that may be usedinclude, but are not limited to, the triggers or sensors disclosedherein and the triggers or sensors disclosed in U.S. Pat. No. 6,851,711to Goertzen et al, United States Patent Application Publication No.2004/0150204, and United States Patent Application Publication No.2005/0151360 to Bertrand et al. Tipping may be sensed in ways that areunrelated to movement of the rear casters relative to the frame.Examples of ways a tipping behavior may be sensed include, but are notlimited to, the ways tipping is sensed in U.S. Pat. No. 6,851,711 toGoertzen et al, United States Patent Application Publication No.2004/0150204, and United States Patent Application Publication No.2005/0151360 to Bertrand et al.

FIG. 2 is a flow chart that illustrates an embodiment of a method 200 ofstabilizing a mid-wheel drive wheelchair frame. In the method, upwardand downward movement of the front casters 108 a, 108 b is allowed(block 202) when at least one rear caster 110 a, 110 b is in a normaloperating position. When both of the rear casters 110 a, 110 b move outof a normal operating position, the front casters 108 a, 108 b arelocked (block 204) against at least upward movement relative to theframe. The front casters 108 a, 108 b may be locked against both upwardand downward movement or only against upward movement.

Normal operating positions of the rear casters 110 a and 110 b includethe positions of the rear casters when the wheelchair is stationary onlevel ground (referred to herein as the stationary, level groundposition). Normal operating positions of the rear casters 110 a and 110b also include any position of the rear casters relative to the framewhere the rear caster(s) are rotated as indicated by arrow 70 in FIG.1B. Normal operating positions of the rear casters 110 a, 110 b alsoinclude any positions where the rear caster(s) are rotated relative tothe frame 102 as indicated by arrow 72 by less than a predetermineddistance or angle below the stationary, level ground position. In theexemplary embodiment, the predetermined distance or angle from thestationary, level ground position in the direction indicated by arrow 72corresponds to a distance or angle that is indicative of a tippingbehavior of the wheelchair. For example, movement of the rear caster(s)relative to the frame in the direction indicated by arrow 72 that isgreater than ½ inch may be indicative of tipping of the wheelchair andout of the normal operating position of the rear casters. However, thenormal operating position of the rear casters 110 a and 110 b will varyfrom one wheelchair to another.

FIGS. 1, 3 and 4 illustrate a 100 wheelchair with a stabilizing assembly114 that inhibits upward movement of the first and second front casters108 a, 108 b with respect to the wheelchair frame 102 based on movementof first and second rear casters 110 a, 110 b with respect to thewheelchair frame. Referring to FIGS. 1A, 1B and 1C, the stabilizingassembly 114 allows upward and downward movement (as indicated by doublearrow 116) of the first and second front casters 108 a, 108 b relativeto the frame 102 when the first and second rear casters 110 a, 110 b arein normal operating positions relative to the frame.

FIGS. 3A, 3B, and 3C illustrate the wheelchair 100 where the rear caster110 a is in a normal operating position and the rear caster 110 b hasdropped below the range of normal operating positions. This conditionmay occur when one of the rear casters falls into a depression 302 asillustrated by FIGS. 3A, 3B, and 3C. This condition may also occur whenthe wheelchair travels laterally along an inclined surface. When therear caster 110 a is in a normal operating position and the rear caster110 b has dropped below the range of normal operating positions, both ofthe stabilizing members 114 continue to allow upward and downwardmovement of the first and second front casters 108 a, 108 b relative tothe frame 102.

FIGS. 4A, 4B, and 4C illustrate the wheelchair 100 exhibiting a tippingbehavior. The frame 102 of the wheelchair 100 is pitched forward towardthe front casters 108 a, 108 b. As a result, the rear casters 110 a, 110b move downward relative to the frame 102 to maintain contact with theground. This downward movement positions both of the rear casters 110 a,110 b below the range of normal operating positions relative to theframe 102. The sensors or triggers 112 sense that the rear casters 110a, 110 b are both below the range of normal operating positions andcause the stabilizing members 114 to engage. In the example illustratedby FIGS. 4A, 4B and 4C, engagement of the stabilizing assemblies locksthe first and second front casters 108 a, 108 b against upward movementrelative to the frame, but allow the front casters to move downward asindicated by arrow 400 when the stabilizing assembly is engaged. Inanother embodiment, the stabilizing assembly 114 locks the front casterpivot arms against both upward and downward movement with respect to thepivot arm when engaged. In another embodiment, engagement of thestabilizing assemblies 114 greatly increase the amount of force requiredto move the front casters upward with respect to the frame. In anotherembodiment, engagement of the stabilizing assemblies 114 causes thestabilizing assemblies to apply additional force to move the frontcasters downward relative to the frame and return the frame to a normaloperating position. When one or more of the rear casters return to anormal operating position relative to the frame, the sensors or triggers112 disengage the stabilizing assembly to allow upward and downwardmovement of the first and second front casters relative to the frame.

The stabilizing member, stabilizing members, or stabilizing assembly 114or assemblies can take a wide variety of different forms. For example,the stabilizing assembly 114 may be a fluid cylinder 500 as illustratedby FIG. 5. One fluid cylinder 500 may be coupled between each frontcaster 108 a, 108 b at connection 501 and the frame 102 at connection503, or a single fluid cylinder may be coupled between the front castersand the frame. As used herein, “coupled” refers to both direct couplingof two or more components or the indirect coupling of components such asthrough one or more intermediary components or structures. The fluidcylinder 500 includes a piston 502, a housing 504 that defines a pistonchamber 506, a rod 508, and a valve 510. The rod 508 extends into thehousing 504 and is connected to the piston. The piston 502 divides thechamber 506 into two compartments 512, 514. The valve 510 selectivelyallows fluid to flow between the two compartments when the valve is openand prevents flow between the two compartments when the valve is closed.As such, the rod 508 can move into and out of the housing 504 when thevalve 510 is open and the position of the piston 502 and the rod issubstantially fixed when the valve is closed. When the valve 510 isopen, the movement of the fluid between the chambers 512, 514 andthrough the valve 510 provides a damping effect. As such, the cylinder500 acts as a shock absorber when the valve is open and damps upward anddownward movement of the front caster. In one embodiment, when the valveis “closed” fluid is allowed flow from the compartment 512 to thecompartment 514, but not from the compartment 514 to the compartment512. As such, the rod 508 may be moved into the housing 504, but not outthe housing when the valve 510 is closed. When the valve 510 is closed,the cylinder 500 damps downward movement of the front caster andinhibits upward movement of the front caster. One acceptable fluidcylinder that may be used is model number Koa8kx-2-06-304/000N fromEasylift.

FIG. 6 illustrates a cylinder 600 that is similar to the cylinder 500illustrated in FIG. 5, but includes a spring 602 that biases or returnsthe rod 508 to a retracted position. In an embodiment where the valveprevents fluid flow between the compartments 512, 514 when the valve isclosed, the actuator 600 biases the front caster toward contact with theground only when the valve 510 is open. In an embodiment where the valveallows flow from the compartment 512 to the compartment 514, but notfrom the compartment 514 to the compartment 512 when the valve isclosed, the actuator 600 biases the front caster toward contact with theground when the valve 510 is open or closed. One acceptable fluidcylinder with a spring return that may be used is model numberk0m2pm2-060-345-002/50N from Easylift.

The stabilizing cylinders 500, 600 illustrated by FIGS. 5 and 6 are twoexamples of the wide variety of different stabilizing assemblies 114that can be used. Any arrangement capable of inhibiting upward and/ordownward movement of a front caster relative to a frame can be used. Asnoted above, any of the arrangements for inhibiting movement of a frontcaster with respect to a frame disclosed in U.S. Pat. No. 6,851,711 toGoertzen et al., United States Patent Application Publication No.:2004/0150204 to Goertzen et al., and United States Patent ApplicationPublication No.: 2005/0151360 to Bertrand et al. can be used.

Stabilizing members or assemblies 114 and triggers or sensors 112 may bearranged in a wide variety of different ways to inhibit further tippingwhen both rear casters 110 a, 110 b drop below the range of normaloperating positions. Referring to FIGS. 7A, 7B, and 7C a trigger orsensor 112 is coupled to each rear caster 110 a, 110 b. A stabilizingmember or assembly 114 is coupled to each front caster 108 a, 108 b. Thestabilizing assemblies 114 are linked by a coupling 700, such that eachstabilizing member or assembly 114 will not engage unless the otherstabilizing assembly also engages. The coupling 700 may take a widevariety of different forms. For example, the coupling 700 may be amechanical linkage, and electronic linkage, an electromechanical linkageor a pneumatic or hydraulic linkage. The stabilizing members orassemblies 114 may be mechanically linked by wire, a rod or a clutchmechanism, electromechanically linked by a pair of solenoid actuatorsthat are in electronic communication. When the stabilizing assemblies114 are fluid actuators, the stabilizing assemblies may be pneumaticallyor hydraulically linked by conduits and valves that connect the chambersof the fluid actuators. For example, fluid devices from Easylift may belinked in this manner.

In the example illustrated by FIGS. 8A, 8B, and 8C a trigger or sensor112 is coupled to each rear caster 110 a, 110 b and a single stabilizingassembly 114 is coupled to both of the front casters 108 a, 108 b. Thestabilizing member or assembly 114 is in communication with bothtriggers or sensors 112, such that the stabilizing assembly 114 will notengage unless both of the triggers or sensors 112 sense a condition thatindicates a tipping behavior of the frame 102, such as downward movementof both rear casters 110 a, 110 b relative to the frame 102. The singlestabilizing assembly 114 may be arranged to permit independent upwardand downward movement of the front casters 108 a, 108 b.

In the examples illustrated by FIGS. 9A, 9B and 9C, a trigger or sensor112 is coupled to each rear caster 110 a, 110 b and a stabilizingassembly 114 is coupled to each front caster 108 a, 108 b. The triggersor sensors 112 are linked by a coupling 900, such that each sensor ortrigger will not cause engagement of its respective stabilizing assembly114 unless both of the sensors or triggers sense a tipping behavior ofthe wheelchair. The coupling 900 may take a wide variety of differentforms. For example, the coupling 900 may be a mechanical linkage, andelectronic linkage, an electromechanical linkage or a pneumatic orhydraulic linkage. The triggers or sensors 112 may be mechanicallylinked by wire or a rod, electromechanically linked by a pair ofsolenoid actuators that are in electronic communication, and/orpneumatically or hydraulically linked by a pair of fluid actuators thatare in fluid communication.

In the example illustrated by FIGS. 10A, 10B, and 10C a single triggeror sensor 112 is coupled to both rear casters 110 a, 110 and a singlestabilizing assembly 114 is coupled to both of the front casters 108 a,108 b. The single stabilizing assembly 114 is controlled by the singletrigger or sensor 112. In one embodiment, the single trigger or sensor112 will not detect a tipping behavior unless both rear casters fallbelow their range of normal operating positions. The single trigger orsensor 112 causes the single stabilizing assembly 114 to engage when atipping behavior is sensed. The single stabilizing assembly 114 may bearranged to permit independent upward and downward movement of the frontcasters 108 a, 108 b when disengaged and independent downward movementof the front casters when engaged.

FIGS. 11, 12 and 13 illustrate a wheelchair 1100 with a rear casterposition sensing linkage 1101 that allows a single trigger or sensor 112to determine when both of the rear casters 110 a, 110 b have droppedbelow their normal operating positions with respect to the frame 102.The linkage 1101 and sensor 112 can be used to control a pair ofstabilizing members 114 as illustrated, or a single stabilizing member(see FIG. 10). The linkage 1101 is pivotally connected to the frame atpivot point 1102. The linkage 1101 includes a rear caster pivot armsensing portion 1104 and a sensor activating portion 1106. The rearcaster pivot arm sensing portion 1104 and a sensor activating portion1106 are pivotable around the pivot point 1102. The sensing portion 1104is in connection with the rear caster pivot arms 120 a, 120 b. Thesensor activating portion 1106 is in communication with the trigger orsensor 112.

Referring to FIGS. 11A, 11B and 11C, when the first and second rearcasters 108 a, 108 b are in normal operating positions, the first andsecond rear caster pivot arms 120 a, 120 b maintain the rear casterpivot arm sensing portion 1104 and the sensor activating portion 1106 ina first or disengaged position shown in FIGS. 11A, 11B, and 11C. Whenthe sensor activating portion 1106 is in the first position, the sensor112 controls the stabilizing assembly 114 to allow upward and downwardmovement (as indicated by double arrow 1116) of the first and secondfront casters 108 a, 108 b relative to the frame 102. In the exampleillustrated by FIGS. 11A, 11B, and 11C, the sensor activating portion1106 is in engagement or close to the sensor in the first or disengagedposition. In another embodiment, the sensor activating portion 1106 isspaced apart from the sensor in the first position or disengagedposition.

FIGS. 12A, 12B, and 12C illustrate the wheelchair 1100 where the rearcaster 110 a is in a normal operating position and the rear caster 110 bhas dropped below the range of normal operating positions. When the rearcaster 110 a is in a normal operating position and the rear caster 110 bhas dropped below the range of normal operating positions, the firstrear caster pivot arms 120 a maintains the rear caster pivot arm sensingportion 1104 and the sensor activating portion 1106 in the first ordisengaged position.

FIGS. 13A, 13B, and 13C illustrate the wheelchair 100 exhibiting atipping behavior. The frame 102 of the wheelchair 100 is pitched forwardtoward the front casters 108 a, 108 b. As a result, the rear casters 110a, 110 b move downward relative to the frame 102 to maintain contactwith the ground. This downward movement positions both of the rearcasters 110 a, 110 b below the range of normal operating positions withrespect to the frame. When the first and second rear casters 108 a, 108b fall below their ranges of normal operating positions, the rear casterpivot arm sensing portion 1104 and the sensor activating portion 1106pivot to a second or engaged position shown in FIGS. 13A, 13B, and 13C.When the sensor activating portion 1106 is in the second or engagedposition, the sensor 112 controls the stabilizing assembly 114 toinhibit at least upward movement of the first and second front casters108 a, 108 b relative to the frame 102. In the example illustrated byFIGS. 13A, 13B, and 13C, the sensor activating portion 1106 is spacedapart from the sensor in the second or engaged position. In anotherembodiment, the sensor activating portion 1106 is in contact or close tothe sensor in the second or engaged position. When one or more of therear casters return to a normal operating position relative to theframe, the linkage 1101 is moved back to the disengaged position and thesensor or trigger 114 causes the stabilizing assembly to disengage andallow upward and downward movement of the front casters relative to theframe.

FIGS. 14, 15 and 16 illustrate a wheelchair 1400 with a rear casterposition sensing linkage 1401 that actuates a pair of triggers orsensors 112 when both of the rear casters 110 a, 110 b have droppedbelow their normal operating positions with respect to the frame 102 anddoes not actuate either of the triggers or sensors 112 when one or moreof the rear casters 110 a, 110 b are in their normal operating positionwith respect to the frame 102. The linkage 1401 and sensors 112 can beused to control a pair of stabilizing members 114 as illustrated, or asingle stabilizing member (see FIG. 8). The linkage 1401 is pivotallyconnected to the frame at pivot point 1402. The linkage 1401 includes arear caster pivot arm sensing portion 1404 and a sensor activatingportion 1406. The rear caster pivot arm sensing portion 1404 and asensor activating portion 1406 are pivotable around the pivot point1402. The sensing portion 1404 is coupled to the rear caster pivot arms120 a, 120 b. The sensor activating portion 1406 is in communicationwith both of the triggers or sensors 112.

Referring to FIGS. 14A, 14B and 14C, when the first and second rearcasters 108 a, 108 b are in normal operating positions, the first andsecond rear caster pivot arms 120 a, 120 b maintain the rear casterpivot arm sensing portion 1404 and the sensor activating portion 1406 ina first or engaged position shown in FIGS. 14A, 14B, and 14C. When thesensor activating portion 1406 is in the first position, the sensoractivating portion 1406 maintains both sensors 112 in a first state. Inthe first state, the two sensors 112 control the stabilizing assemblies114 to allow upward and downward movement (as indicated by double arrow1416) of the first and second front casters 108 a, 108 b relative to theframe 102.

FIGS. 15A, 15B, and 15C illustrate the wheelchair 1400 where the rearcaster 110 a is in a normal operating position and the rear caster 110 bhas dropped below the range of normal operating positions. When the rearcaster 110 a is in a normal operating position and the rear caster 110 bhas dropped below the range of normal operating positions, the firstrear caster pivot arm 120 a maintains the rear caster pivot arm sensingportion 1404 and the sensor activating portion 1106 in the first ordisengaged position.

FIGS. 16A, 16B, and 16C illustrate the wheelchair 1400 exhibiting atipping behavior. The rear casters 110 a, 110 b move downward, below therange of normal operating positions relative to the frame. When thefirst and second rear casters 108 a, 108 b fall below their ranges ofnormal operating positions, the rear caster pivot arm sensing portion1404 and the sensor activating portion 1406 move to a second or engagedposition shown in FIGS. 16A, 16B, and 16C. When the sensor activatingportion 1406 is in the second or engaged position, the sensor activatingportion 1406 places both sensors 112 in a second state. In the secondstate, the sensors 112 control the stabilizing assemblies 114 to inhibitat least upward movement of the first and second front casters 108 a,108 b relative to the frame 102. When one or more of the rear castersreturn to a normal operating position relative to the frame, the linkage1401 is moved back to the disengaged position and both sensors ortriggers 114 cause the stabilizing assemblies 114 to disengage and allowupward and downward movement of the front casters relative to the frame.

FIGS. 17, 18 and 19 illustrate an embodiment of a rear caster suspension1700 with a rear caster position sensing arrangement 1706. The rearcaster suspension 1700 includes a pair of rear caster assemblies 1702 a,1702 b, a pair of sensors or triggers 1704 a, 1704 b, the rear casterposition sensing arrangement 1706, and a pair of biasing members 1708 a,1708 b, such as springs or other resilient members. The rear casterposition sensing arrangement 1706 is in communication with both rearcaster assemblies 1702 a, 1702 b. When one or both of the rear casters1702 a, 1702 b are in a normal operating position, the rear casterposition sensing arrangement communicates this condition to both sensorsor triggers 1704 a, 1704 b. When both of the rear casters 1704 a, 1704 bfall below their normal operating positions, the rear castor positionsensing arrangement communicates this condition to both sensors ortriggers 104 a and 104 b. As a result, both sensors or triggers 1704 a,1704 b are placed in an engaged state when both rear casters 1702 a,1702 b fall below their normal operating positions and both sensors ortriggers 1704 a, 1704 b are placed in a disengaged state when one orboth of the rear casters are in a normal operating position. Theconditions of the rear casters can be communicated by the rear casterposition sensing arrangement in a wide variety of different ways. Forexample, the rear caster position sensing arrangement may be amechanical linkage or assembly that communicates the condition of therear casters to the sensors, as illustrated by FIGS. 17A-17C.

In the example illustrated by FIGS. 17, 18 and 19, compression springsare schematically represented. However, extension springs can be used,or the biasing members can take some other form. Each rear casterassembly 1702 includes a caster 1710 and a pivot arm 1712. The castor1710 is rotatable about an axis 1714 with respect to the pivot arm 1712.The pivot arms 1712 are coupled to a wheelchair frame 1701 (See FIG.17B) at pivots 1716 a, 1716 b. The sensors or triggers 1704 a, 1704 bare supported by the wheelchair frame 1701.

The illustrated rear caster position sensing arrangement 1706 includes apair of spaced apart trigger actuating members 1720 a, 1720 b that arecoupled to the wheelchair frame 1701 at pivots 1722 a, 1722 b. Thetrigger actuating members 1720 a, 1720 b are connected together by a bar1724. The biasing members 1708 a, 1708 b are interposed between the rearcaster assemblies 1702 a, 1702 b and the trigger actuating members 1720a, 1720 b.

The rear caster suspension 1700 and rear caster position sensingarrangement 1706 can be included on any type of wheelchair to sense atipping behavior and control one or more stabilizing members or astabilizing assembly to inhibit further tipping. Referring to FIGS. 17A,17B and 17C, when the rear caster assemblies 1702 a, 1702 b are innormal operating positions relative to the frame, 1701, the biasingmembers 1708 a, 1708 b are compressed between the trigger actuatingmembers 1720 a, 1720 b and the rear caster pivot arms 1712 a, 1712 b.The biasing members 1708 a, 1708 b force the trigger actuating members1708 a, 1708 b into engagement with the sensors or triggers 1704 a, 1704b to place both of the sensors in a depressed or disengaged state.

FIGS. 18A and 18B illustrate the rear caster suspension 1700 and rearcaster position sensing arrangement 1706 where the rear caster assembly1702 b is in a normal operating position and the rear caster assembly1702 a has dropped below the range of normal operating positions. Thiscondition may occur when the wheelchair travels laterally along aninclined surface 1800. This condition may also occur when one of therear casters falls into a depression (see FIGS. 3A, 3B, and 3C). Whenthe rear caster assembly 1702 b is in a normal operating position andthe rear caster assembly 1702 a has dropped below the range of normaloperating positions, the biasing member 1708 b remains compressedbetween the trigger actuating member 1720 b and the rear caster pivotarms 1712 b, while the biasing member 1708 a extends to a relaxed state(See FIG. 18B). The biasing member 1708 b forces the trigger actuatingmember 1720 b into engagement with the sensor or trigger 1704 b. The bar1724 that connects the trigger actuating member 1720 a to the triggeractuating member 1720 b holds the trigger actuating member 1720 a inengagement with the sensor or trigger 1704 a. The trigger actuatingmembers 1720 a, 1720 b place both of the sensors in a depressed ordisengaged state when the rear casters are in the positions shown inFIGS. 18A and 18B.

FIGS. 19A and 19B illustrate the rear caster suspension 1700 and rearcaster position sensing arrangement 1706 where the rear casterassemblies 1702 a, 1702 have both dropped below the range of normaloperating positions. This condition may occur when the wheelchairexhibits a tipping behavior. When both of the rear caster assemblies1702 a, 1702 b have dropped below the range of normal operatingpositions, the biasing members 1708 a, 1708 b both extend to a relaxedstate and may pull the trigger actuating members 1708 a, 1708 b out ofengagement with the sensors or triggers 1704 a, 1704 b to place thesensors or triggers in an engaged state. When one or more of the casterassemblies 1702 a, 1702 b return to a normal operating position withrespect to the frame 1701, both sensors or triggers are returned to thedisengaged state.

FIGS. 20, 21 and 22 illustrate an embodiment of a rear caster suspension2000 and rear caster position sensing arrangement 2006 where movement ofone caster assembly 2002 a is limited, depending on the position of thesecond caster assembly 2002 b. The rear caster suspension includes apair of rear caster assemblies 2002 a, 2002 b, a pair of sensors ortriggers 2004 a, 2004 b, the rear caster position sensing arrangement2006, and a pair of biasing members 2008 a, 2008 b, such as springs orother resilient members. In the example illustrated by FIGS. 20, 21 and22, compression springs are schematically represented. However,extension springs can be used, or the biasing members can take someother form. Each rear caster assembly 2002 includes a caster 2010, apivot arm 2012 a, 2012 b, and a stop member 2013 a, 2013 b attached tothe pivot arm. The pivot arms 2012 are coupled to a wheelchair frame2001 at pivots 2016 a, 2016 b (See FIG. 20B). The stop members 2013 a,2013 b rotate with the pivot arms 2012 a, 2012 b about the pivots 2016a, 2016 b. The sensors or triggers 2004 a, 2004 b are supported by thewheelchair frame 2001.

The illustrated rear caster position sensing arrangement 2006 includes apair of spaced apart trigger actuating members 2020 a, 2020 b that arecoupled to the wheelchair frame 2001 at pivots 2022 a, 2022 b. Theelongated members 2020 a, 2020 b are connected together by a bar 2024.The bar 2024 extends past the pivots 2022 a, 2022 b for selectiveengagement with the stop members 2013 a, 2013 b. The biasing members2008 a, 2008 b are interposed between the rear caster assemblies 2002 a,2002 b and the trigger actuating members 2020 a, 2020 b.

The rear caster suspension 2000 and rear caster position sensingarrangement 2006 operate to place the sensors in the disengaged andengaged states based on the positions of the rear caster assemblies 2002a, 2002 b. The rear caster suspension 2000 and rear caster positionsensing arrangement 2006 limit the relative positions of the rear casterassemblies 2002 a, 2002 b. In one embodiment, the suspension arrangement2000 does not include a rear caster position sensing arrangement, andthe sensors 2004 a, 2004 b are omitted. In this embodiment, theelongated members 2020 a, 2020 b may be modified accordingly or replacedwith a different arrangement for coupling the biasing members 2008 a,2008 b to the bar 2024.

Referring to FIGS. 20A, 20B and 20C, when one or both of the rear casterassemblies 2002 a, 2002 b are in normal operating positions relative tothe frame 2001, the biasing members 2008 a, 2008 b hold the triggeractuating members 2020 a, 2020 b against the sensors or triggers 2004 a,2004 b (or some other stop if the sensors are omitted). The triggeractuating members 2020 a, 2020 b position the bar 2024 with respect tothe stop members 2013. As long as the force applied by one or more ofthe biasing members 2008 a, 2008 b is sufficient to maintain the triggeractuating members 2020 a, 2020 b against the sensors or triggers 2004 a,2004 b, the position of the bar 2024 is fixed. When there is a gap 2025(FIG. 20B) between the bar 2024 and the stop members 2013 a, 2013 b, thecaster assemblies 2002 are free to move upwardly and downwardly withrespect to one another.

FIGS. 21A and 21B illustrate the situation where the rear casterassembly 2002 b drops, such that the stop member 2013 b rotates intocontact with the bar 2024. When the stop member 2013 b engages the bar2024, further movement of the rear caster assembly 2002 b is inhibitedby the bar. Referring to FIGS. 22A and 22B, the bar 2024 prevents thecaster assembly 2002 a from falling into a deep depression. The rearcaster assembly 2002 a can be moved downward by applying a downwardforce indicated by arrow 2050 in FIGS. 22A and 22B. The force is appliedby the stop member 2013 b, to the bar 2024, and to the trigger actuatingmember 2020 b. If the force applied to trigger actuating member 2020 ais sufficient to compress the biasing member 2008 b, the triggeractuating member 2020 b moves toward the rear caster pivot arm 2012 b.As a result, the elongated members 2020 a, 2020 b may move away from thetriggers or sensors 2004 a, 2004 b. When both rear casters 1010 fallaway from the frame 2001, the sensors 2004 a, 2004 b are placed in theengaged state in the same manner as described with respect to the rearcaster suspension and trigger arrangement 1700. When one or both of therear casters are in a normal operating position, the sensors 2004 a,2004 b are placed in a disengaged state in the same manner as describedwith respect to the rear caster suspension and trigger arrangement 1700.

FIGS. 23 and 24 illustrate another embodiment of a rear castersuspension 2300 with a rear caster position sensing arrangement 2306.The rear caster suspension includes a rear caster assembly 2302, a pairof sensors or triggers 2304 a, 2304 b, the rear caster position sensingarrangement 2306, and a biasing member 2308, such as a spring. In theexample illustrated by FIGS. 23 and 24, a compression spring isschematically represented. However, an extension spring can be used, orthe biasing member can take some other form.

The rear caster assembly 2302 includes a pair of casters 2310 a, 2310 band a pivot arm 2312. The pivot arm 2312 includes a first member 2313coupled to a wheelchair frame 2301 at a pivot 2316 (See FIG. 23B) and asecond member 2315 connected to the first member 2313, such that thepivot arm 2312 has a generally “T-shaped” configuration. The castors2310 a, 2310 b are connected to ends of the second member 2315 and arerotatable with respect to the pivot arm 2312.

The sensors or triggers 2304 a, 2304 b are supported by the wheelchairframe 2301. The illustrated rear caster position sensing arrangement2306 includes a pair of spaced apart elongated members 2319 a, 2319 b(See FIG. 23A) that support a trigger actuating member 2320 and arecoupled to the wheelchair frame 2301 at pivots 2322 a, 2322 b. The rearcaster position sensing arrangement 2306 could also be configured toinclude only one member (or any other number of members) member thatsupports the rear caster position sensing arrangement 2306. The biasingmember 2308 is interposed between the rear caster assembly 2302 and thetrigger actuating member 2320.

The rear caster suspension 2300 with the rear caster position sensingarrangement 2306 can be included on any type of wheelchair to sense atipping behavior and control one or more stabilizing members orstabilizing assemblies. Referring to FIGS. 23A, 23B and 23C, when therear caster assembly 2302 is in a normal operating position relative tothe frame 2301, the biasing member 2308 is compressed between thetrigger actuating member 2320 and the rear caster pivot arm 2312. Thebiasing members 2308 force the trigger actuating member 2308 intoengagement with both of the sensors or triggers 2304 a, 2304 b to placeboth of the sensors in a depressed or disengaged state.

FIGS. 24A, 24B and 24C illustrate the rear caster suspension 2300 andthe rear caster position sensing arrangement 2306 where one of the rearcasters 2310 a of the rear caster assembly 2302 a encounters adepression in the support surface. Since both rear casters 2310 a, 2310b are coupled to a common pivot arm, the rear caster 2310 a does notdrop into the depression. The biasing member 2308 remains compressedbetween the trigger actuating member 2320 and the rear caster pivot arms2312 a. The biasing member 2308 forces the trigger actuating member 1708into engagement with the sensors or triggers 2304 a, 2304 b. When therear caster assembly 2302 drops below the range of normal operatingpositions, the biasing member 2308 extends to a relaxed state and maypull the trigger actuating member 2308 out of engagement with thesensors or triggers 1704 a, 1704 b to place the sensors or triggers inan engaged state.

FIGS. 25A, 25B and 25C illustrate a rear caster suspension 2500 that isa variation of the rear caster suspension 2300 where the second member2315 of the pivot arm is pivotally connected to the first member 2313 bya pivotal connection 2500. The pivotal connection allows the ends of thesecond member 2315 and the attached rear casters 2310 a, 2310 b to moveupward and downward with respect to one another. When one rear caster2310 a moves down, the other rear caster 2310 b moves up.

Stability systems can be used on a wide variety of vehicles. When usedon wheelchairs, the wheelchairs may include front caster pivot arms ofany configuration. The front caster pivot arms may be coupled to driveassemblies or the front caster pivot arms may be independent of thedrive assemblies (See FIGS. 1A, 1B, 1C). The front caster pivot arms canbe coupled to the drive assemblies in a wide variety of different ways.For example, the front caster pivot arms can be coupled to the driveassembly in any manner that transfers motion of the drive assembly tothe front caster pivot arm, including but not limited to, a fixed lengthlink, a variable length link, a flexible link, a chain, a cord, a belt,a wire, a gear train, or any other known structure for transferringmotion from one structure to another structure. FIGS. 26-31 illustrateone side of wheelchairs with stability systems and pivot arms that arecoupled to a drive assembly. The other side is a mirror image in theexemplary embodiment and is therefore not described in detail.

FIG. 26 schematically illustrates a mid-wheel drive wheelchair 2600 thatincludes a tip or stability control system that comprises at least onetip sensor or trigger 2612 and at least one stabilizing member orassembly 2614. The wheelchair 2600 includes front caster pivot arms 2608that are coupled to drive assemblies 2606. Each drive assembly 2606includes a drive wheel 2615 and a motor or drive 2617 that propels thedrive wheel 2615. The drive 2617 may comprise a motor/gear boxcombination, a brushless, gearless motor, or any other known arrangementfor driving the drive wheel 2615. The drive assembly 2606 is connectedto the frame 2602 at a pivotal connection 2619. In the exampleillustrated by FIG. 26, the pivotal connection 2619 is disposed below adrive axis 2621 of the drive wheel 2615 when the wheelchair 2600 isresting on flat, level ground.

A front caster pivot arm 2608 is connected to each drive assembly 2606.A front caster 2631 is coupled to each front caster pivot arm 2608. Thefront caster 2631 is movable upwardly and downwardly as indicated bydouble arrow 2616 by pivotal movement of the drive 2617 about thepivotal connection 2619. Torque applied by the drive assembly 2606 urgesthe front caster pivot arm 2608 and the front caster 2631 upward withrespect to a support surface 2633 as indicated by arrow 2635. In oneembodiment, the torque applied by the drive assembly 2606 lifts thefront caster 2631 off the support surface 2633. In another embodiment,the torque applied by the drive assembly 2606 urges the front caster2631 upward, but does not lift the front caster up off of the supportsurface.

Rear casters 2610 are coupled to the frame 2602 such that the rearcasters are moveable upwardly and downwardly with respect to the frame.A stabilizing assembly 2614 is coupled to each front caster pivot arm2618 and to the frame 2602. However, the stabilizing assembly can takeany form that allows the stabilizing assembly to inhibit tippingbehavior. One or more triggers or sensors 2612 may be coupled to rearcaster pivot arms 2620 to detect a tipping behavior of the wheelchair.However, a trigger or sensor can be arranged in any manner to detect atipping behavior of the wheelchair and need not be coupled to a rearcaster. The trigger or sensor 2612 senses when conditions exist that maycause the vehicle to exhibit a tipping behavior and causes the lockingassembly 2614 to engage when a tipping behavior is sensed to prevent anyfurther tipping behavior.

FIG. 27 schematically illustrates a mid-wheel drive wheelchair 2700 thatincludes a tip or stability control system that comprises at least onetip sensor or trigger 2712 and at least one stabilizing member orassembly. The wheelchair 2700 is similar to the wheelchair 2600 of FIG.26, but each front caster pivot arm 2708 includes upper and lower links2710 a, 2710 b that define a four bar linkage. The upper link 2710 a ispivotally coupled to a caster support member 2711 at a pivotalconnection 2780 and is fixedly connected to the drive 2617. The lowerlink 2710 b is pivotally coupled to the caster support member 2711 at apivotal connection 2782 and is pivotally connected to the frame 2701 ata pivotal connection 2783.

The drive 2617, the links 2710 a, 2710 b, the frame 2701, and the castersupport member 2711 form a four-bar linkage. The pivotal connections2619, 2780, 2782, 2783 can be positioned at a wide variety of differentlocations on the frame 2701 and the caster support member 2711 and thelength of the links 2706 can be selected to define the motion of thefront caster as the front caster pivot arm 2708 is pivoted.

The rear casters 2710 are coupled to the frame 2701 such that the rearcasters are moveable upwardly and downwardly with respect to the frame.A stabilizing assembly 2714 is coupled to each front caster pivot arm2718 and to the frame 2702. However, the stabilizing assembly can takeany form and be coupled in any manner that allows the stabilizingassembly to inhibit tipping behavior. For example, a stabilizingassembly 2714 can be coupled to the drive 2617. One or more triggers orsensors 2712 are coupled to the rear caster pivot arms 2720 to detect atipping behavior of the wheelchair. However, a trigger or sensor can bearranged in any manner to detect a tipping behavior of the wheelchairand need not be coupled to a rear caster. The trigger or sensor 2712senses when conditions exist that may cause the vehicle to exhibit atipping behavior and causes the locking assembly 2714 to engage when atipping behavior is sensed to prevent any further tipping behavior.

FIG. 28 schematically illustrates a mid-wheel drive wheelchair 2800 thatincludes a tip or stability control system 2802 that comprises at leastone tip sensor or trigger 2812 and at least one stabilizing member orassembly. Front caster pivot arms 2808 are coupled to drive assemblies2806 by a link 2809. The wheelchair 2800 is similar to the wheelchair2600 of FIG. 26, but the front caster pivot arm 2808 is pivotallycoupled to the frame 2801 and is coupled to the drive assembly 2806 bythe link 2809. Each drive assembly 2806 is mounted to the frame 2801 bya pivot arm 2820 at a drive assembly pivot axis 2822. The pivot arm 2820extends forward and downward from the motor drive to the drive assemblypivot axis 2822. The pivot axis 2822 of the drive assembly pivot arm2820 is below the drive wheel axis of rotation 2830 and the axis 2832 ofan axle 2834 that the front caster wheel 2836 rotates around.

In one embodiment, a biasing member, such as a spring may optionally becoupled between the frame 2801 and the front caster pivot arm 2808and/or the frame and the drive assembly 2806 to bias the front casterinto engagement with the support surface 2819 or a biasing member may beincluded in the stabilizing assembly 2814. The front caster pivot arm2808 is pivotally mounted to the frame at a pivot axis 2850. The pivotaxis 2850 of the front caster pivot arm 2808 is forward of the driveassembly pivot axis 2822 and below the axis of rotation 2830 of thedrive wheel.

The link 2809 is connected to the drive assembly pivot arm 2820 at apivotal connection 2851 and is connected to the front caster pivot arm2808 at a pivotal connection 2852. The link 2809 can take a wide varietyof different forms. For example, the link may be rigid, flexible, orextendible in length. The link need not comprise a linear member forexample, the link may be a gear train. The link 2809 may be anymechanical arrangement that transfers at least some portion of motion inat least one direction of the drive assembly 2806 to the front casterpivot arm 2808.

When the drive assembly 2806 is accelerated such that the moment armgenerated by drive wheel 2815 is greater then all other moment armsaround pivot axis 2822, the drive assembly 2806 pivots and pulls thelink 2809. Pulling on the link 2809 causes the front caster pivot arm2808 to move upward or urges the pivot arm upward. When the link 2809 isa variable length link, such as a spring, a shock absorber, or a shockabsorber with a spring return, the drive assembly 2806 pulls the link2809 to extend the link to its maximum length or a length where thefront caster pivot arm 2808 begins to pivot. Once extended, the link2809 pulls the front caster pivot arm 2808 upward or urges the frontcaster pivot arm upward.

Rear casters 2810 are coupled to the frame 2801 such that the rearcasters are moveable upwardly and downwardly with respect to the frame.A stabilizing assembly 2814 is coupled to each front caster pivot arm2808 and to the frame 2801, to the drive assembly 2806 and the frame2801 and/or to the link 2809 and the frame 2801. However, thestabilizing assembly can take any form and be positioned in any mannerthat allows the stabilizing assembly to inhibit a tipping behavior. Oneor more triggers or sensors 2812 are coupled to the rear caster pivotarms 2820 to detect a tipping behavior of the wheelchair. However, atrigger or sensor can take any form and be arranged in any manner todetect a tipping behavior of the wheelchair and need not be coupled to arear caster. The trigger or sensor 2812 senses when conditions existthat may cause the vehicle to exhibit a tipping behavior and causes thelocking assembly 2814 to engage when a tipping behavior is sensed toprevent any further tipping behavior.

FIG. 29 schematically illustrates a mid-wheel drive wheelchair 2900 thatincludes a tip or stability control system that comprises at least onetip sensor or trigger 2912 and at least one stabilizing member orassembly 2914. Front caster pivot arms 2908 are coupled to driveassemblies 2906 by a link 2909. The wheelchair 2900 is similar to thewheelchair 2800 of FIG. 28, but the front caster pivot arm 2908 and thedrive assembly pivot arm 2920 are disposed in a crossed configuration.

Each drive assembly 2906 is mounted to a frame 2901 by a pivot arm 2920at a drive assembly pivot axis 2922. The pivot arm 2920 extends forwardand downward from the motor drive to the drive assembly pivot axis 2922.The pivot axis 2922 of the drive assembly pivot arm 2920 is below thedrive wheel axis of rotation 2930. The front caster pivot arm 2908 ispivotally mounted to the frame at a pivot axis 2949. The pivot axis 2949of the front caster pivot arm 2908 is rearward of the drive assemblypivot axis 2932 and below the axis of rotation 2930 of the drive wheel.As such, the front caster pivot arm 2908 and the drive assembly pivotarm 2920 are in a crossed configuration. The front caster pivot arm 2908and the drive assembly pivot arm 2920 may be bent or may be offset toaccommodate the crossed configuration.

The link 2909 is connected to the drive assembly pivot arm 2920 at apivotal connection 2950 and is connected to the front caster pivot arm2908 at a pivotal connection 2952. The link 2909 can take a wide varietyof different forms. Any link 2909 that transfers at least some portionof motion in at least one direction of the drive assembly 2906 to thefront caster pivot arm 2908 can be used.

When the drive assembly 2906 is accelerated such that the moment armgenerated by a drive wheel 2915 is greater then all other moment armsaround pivot axis 2922, the drive assembly 2906 pivots and pulls thelink 2909. Pulling on the link 2909 causes the front caster pivot arm2908 to move upward or urges the pivot arm upward.

Rear casters 2910 are coupled to the frame 2901 such that the rearcasters are moveable upwardly and downwardly with respect to the frame.A stabilizing assembly 2914 is coupled to each front caster pivot arm2908 and to the frame 2901, to the drive assembly 2906 and the frame2901 and/or to the link 2909 and the frame 2901. One or more triggers orsensors 2912 are coupled to rear caster pivot arms 2920 to detect atipping behavior of the wheelchair. However, a trigger or sensor cantake any form and be arranged in any manner to detect a tipping behaviorof the wheelchair and need not be coupled to a rear caster. The triggeror sensor 2912 senses when conditions exist that may cause the vehicleto exhibit a tipping behavior and causes the locking assembly 2914 toengage when a tipping behavior is sensed to prevent any further tippingbehavior.

FIG. 30 schematically illustrates a mid-wheel drive wheelchair 3000 thatincludes a tip or stability control system that comprises at least onetip sensor or trigger 3012 and at least one stabilizing member orassembly 2914. Front caster pivot arms 3008 are coupled to driveassemblies 3006 by a link 3009. The wheelchair 3000 is similar to thewheelchair 2900 of FIG. 29, but the front caster pivot arm 3008comprises an upper link 3011 a and a lower link 3011 b.

The upper link 3011 a is pivotally coupled to a caster support member3013 at a pivotal connection 3015 and is pivotally connected to theframe 3001 at a pivotal connection 3017. The lower link 3011 b ispivotally coupled to the caster support member 3013 at a pivotalconnection 3019 and is pivotally connected to the frame 3001 at apivotal connection 3021.

The caster support member 3013 may be any structure that couples thelinks 3011 a, 3011 b to be coupled to a front caster 3036. The links3011 a, 3011 b, the frame 3001, and the caster support member 3013 forma four-bar linkage. The pivotal connections 3015, 3017, 3019, 3021 canbe positioned at a wide variety of different locations on the frame 3001and the caster support member 3013 and the length of the links 3011 a,3011 b can be selected to define the motion of the caster 3036 as thefront caster pivot arm 3008 is pivoted. In the example illustrated byFIG. 30, the front caster pivot arm 3008 retracts the front caster 3008or pivots the wheel of the front caster toward the frame as the pivotarm 3008 is lifted and extends the front caster or pivots the wheel ofthe front caster away from the frame as the front caster pivot arm islowered.

Each drive assembly 3006 is mounted to the frame 3001 by a pivot arm3020 at a drive assembly pivot axis 3022. The pivot arm 3020 extendsforward and downward from the motor drive to the drive assembly pivotaxis 3022. The pivot axis 3022 of the drive assembly pivot arm 3020 isbelow the drive wheel axis of rotation 3030 and is in front of the frontcaster pivot arms 3008. As such, the front caster pivot arm 3008 and thedrive assembly pivot arm 3020 are in a crossed configuration. The frontcaster pivot arm 3008 and the drive assembly pivot arm 3020 may be bentor may be offset to accommodate the crossed configuration.

The link 3009 is connected to the drive assembly pivot arm 3020 at apivotal connection 3050 and is connected to the front caster pivot arm3008 at a pivotal connection 3052. The link 3009 can be connected to theupper link 3011 a, or the lower link 3011 b. Any link 3009 thattransfers at least some portion of motion in at least one direction ofthe drive assembly 3006 to the front caster pivot arm 3008 can be used.

When the drive assembly 3006 is accelerated the drive assembly 3006 maypivot and pull the link 3909. Pulling on the link 3009 causes the frontcaster pivot arm 3008 to move upward or urges the pivot arm upward.

Rear casters 3010 are coupled to the frame 3001 such that the rearcasters are moveable upwardly and downwardly with respect to the frame.A stabilizing assembly 3014 is coupled to each front caster pivot arm3008 and to the frame 3001, to the drive assembly 3006 and the frame3001 and/or to the link 3009 and the frame 3001. One or more triggers orsensors 3012 are coupled to rear caster pivot arms 3020 to detect atipping behavior of the wheelchair. However, a trigger or sensor cantake any form and can be arranged in any manner to detect a tippingbehavior of the wheelchair and need not be coupled to a rear caster. Thetrigger or sensor 3012 senses when conditions exist that may cause thevehicle to exhibit a tipping behavior and causes the locking assembly3014 to engage when a tipping behavior is sensed to inhibit furthertipping behavior.

FIG. 31 schematically illustrates a mid-wheel drive wheelchair 3100 thatincludes a tip or stability control system that comprises at least onetip sensor or trigger 3112 and at least one stabilizing or assembly3114. Front caster pivot arms 3108 are coupled to drive assemblies 3106by a link 3109. The wheelchair 3100 is similar to the wheelchair 2800 ofFIG. 28, but the front caster pivot arm 3108 and the drive assembly 3106are pivotally coupled to the frame 3101 at a common pivot axis 3122.

Each drive assembly 3106 is mounted to the frame 3101 by a pivot arm3120. The pivot arm 3120 extends forward and downward from the motordrive to the common pivot axis 3122. The pivot axis 3122 is below thedrive wheel axis of rotation 3130 and the axis 3132 that the frontcaster wheel 3136 rotates around.

The link 3109 is connected to the drive assembly pivot arm 3120 at apivotal connection 3150 and is connected to the front caster pivot arm3108 at a pivotal connection 3152. The link 3109 can take a wide varietyof different forms. For example, the link may be rigid, flexible, orextendible in length. Any link 3109 that transfers at least some portionof motion in at least one direction of the drive assembly 3106 to thefront caster pivot arm 3108 can be used.

When the drive assembly 3106 is accelerated, the drive assembly 3106 maypivot and pull on the link 3109. Pulling on the link 3109 causes thefront caster pivot arm 3108 to move upward or urges the pivot armupward.

Rear casters 3110 are coupled to the frame 3101 such that the rearcasters are moveable upwardly and downwardly with respect to the frame.A stabilizing assembly 3114 is coupled to each front caster pivot arm3108 and to the frame 3101, to the drive assembly 3106 and the frame3101 and/or to the link 3109 and the frame 3101. However, thestabilizing assembly can take any form and be positioned in any mannerthat allows the stabilizing assembly to inhibit tipping behavior. One ormore triggers or sensors 3112 are coupled to the rear caster pivot arms3110 to detect a tipping behavior of the wheelchair. However, a triggeror sensor can take any form and be arranged in any manner to detect atipping behavior of the wheelchair and need not be coupled to a rearcaster. The trigger or sensor 3112 senses when conditions exist that maycause the vehicle to exhibit a tipping behavior and causes the lockingassembly 3114 to engage when a tipping behavior is sensed to prevent anyfurther tipping behavior.

FIGS. 32-37 illustrate an example of a mid-wheel drive wheelchair 3200that includes a control system that comprises sensors or triggers 3212a, 3212 b and stabilizing members 3214 a, 3214 b. The wheelchair 3200includes a frame 3202, a seat (not shown) is supported by the frame3202, first and second drive assemblies 3206 a, 3206 b, first and secondfront caster pivot arms 3218 a, 3218 b, first and second front casters3208 a, 3208 b, first and second rear caster pivot arms 3220 a, 3220 b,and first and second rear casters 3210 a, 3210 b. A rear caster positionsensing arrangement 4400 (see FIGS. 44-51) communicates a condition ofthe rear caster pivot arms 3220 a, 3220 b to both of the sensors ortriggers 3212 a, 3212 b.

Referring to FIG. 32, the illustrated frame 3202 is made from sheetmetal panels, but can be constructed in any manner that is suitable forthe application of the wheelchair 3200. The illustrated frame 3202defines an interior space 3203 for batteries (not shown), wiring (notshown), and other wheelchair components.

Referring to FIGS. 32 and 33, each drive assembly 3206 a, 3206 bincludes a drive wheel 3215 and a motor or drive 3217 that propels thedrive wheel 3215. The drive 3217 may comprise a motor/gear boxcombination, a brushless, gearless motor, or any other known arrangementfor driving the drive wheel 3215. The drive 3717 is coupled to the frame3202 at a pivotal connection 3219. The pivotal connection 3219 isdisposed below a drive axis 3221 of the drive wheel 3215 when thewheelchair 3200 is resting on flat, level ground. FIGS. 38-41 show thewheelchair 3200 with many of the components removed to more clearlyillustrate the drive 3217, the front pivot caster pivot arm 3218 a, therear caster pivot arm 3220 a, and the stabilizing member 3214 a mountedon one side of the frame 3202. The component mounting on the other sideof the frame 3202 may be a mirror image, and is therefore not describedin detail.

Referring to FIG. 39, each front caster pivot arm 3218 a, 3218 bincludes upper and lower links 3223 a, 3223 b that define a four barlinkage. The upper link 3223 a is pivotally coupled to a caster supportmember 3211 at a pivotal connection 3280 and is fixedly connected to thedrive 3217. The lower link 3223 b is pivotally coupled to the castersupport member 3211 at a pivotal connection 3282 and is pivotallyconnected to the frame 3202 at a pivotal connection 3283. The drive3217, the links 3223 a, 3223 b, the frame 3202, and the caster supportmember 3211 form a four-bar linkage.

The front caster 3208 a is coupled to the caster support member 3211.The front caster pivot arms 3218 a, 3218 b are independently pivotableupwardly and downwardly on the opposite sides of the frame to move thefront casters 3208 a, 3208 b upwardly and downwardly with respect to theframe 3202.

Referring to FIGS. 33 and 39, when the drive assembly 3206 a isaccelerated such that the moment arm generated by drive wheel 3215 isgreater then all other moment arms around pivot axis 3219, the driveassembly 3206 pivots about pivot axis 3219 to move the front casterpivot arm 3218 upward or urges the pivot arm upward as indicated byarrow 3301. Resulting upward tendencies of the front caster 3208 a helpsthe wheelchair 3200 to traverse obstacles. In the exemplary embodiment,the drive assembly 3206 b operates in the same manner or a similarmanner to move or urge the front caster 3208 b upward.

Referring to FIGS. 40-42, the stabilizing member 3214 a comprises ahydraulic cylinder with a spring return (see also FIGS. 5 and 6). Thestabilizing member 3214 a includes a housing 4004, and a rod 4008. Inthis embodiment, the sensor or trigger 3212 a is a portion of a button4006 that extends from the stabilizing member 3214 a. The position ofthe button 4006 determines the state of the stabilizing member 3214 a.In the wheelchair 3200, when the button 4006 is depressed, the rod 4008may move into and out of the housing 4004 to extend and shorten thelength of the stabilizing member 3214 a. When the button 4006 isextended, the rod 4008 may move out of the housing 4004 to extend thelength of the stabilizing member 3214 a, but is prevented from movinginto the housing 4004 to shorten the length of the stabilizing member.When the button 4006 is in the depressed position, the movement of thefluid in the stabilizing member 3214 a when the rod extends and retractsprovides a damping effect. When the button 4006 is extended, thestabilizing member damps downward movement of the front caster. In thewheelchair 3200, a spring return (See FIG. 6) biases or returns the rod4008 to an extended position to bias the front caster toward contactwith the ground.

Referring to FIGS. 40-42, the stabilizing member 3214 a is pivotallyconnected to the frame 3202 at a pivotal connection 4020 and to thedrive assembly/front caster pivot arm at a pivotal connection 4022. Whenthe button 4006 is extended, the stabilizing member 3214 a can extend toallow the front caster to move downward with respect to the frame 3202,but cannot retract to prevent upward movement of the front caster withrespect to the frame. When the button 4006 is depressed, the stabilizingmember 3214 a allows the front caster to move upward and downward withrespect to the frame.

Referring to FIG. 42, the pivotal connection 4020 may comprise a ball4030 and socket 4032 connection. The ball 4030 is mounted to the rod4008. The socket 4032 is connected to the frame 3202. If the pivotalconnection 4020 is made before the pivotal connection 4022, the ball4030 can be turned in the socket 4032 to facilitate alignment requiredto make the pivotal connection 4022. If the pivotal connection 4022 ismade before the connection 4022, the ball 4030 can be assembled in thesocket 4022, regardless of the orientation of the ball with respect tothe socket. As a result, assembly of the stabilizing members 3214 a,3214 b to the frame and to the drive assembly/front caster pivot arm ismade easier.

In the embodiment of wheelchair 3200, optional vibration dampingassemblies 4250 are coupled to the button 4006 of each stabilizingmember 3214 a, 3214 b to prevent vibration of the button 4006 in the rod4008. FIG. 42 illustrates a vibration damping assembly 4250 thatincludes a ball portion for a ball and socket connection. FIG. 43illustrates a vibration damping assembly 4250 where the ball is omittedand the stabilizing member 3214 a is connected to the frame by aconventional pivotal coupling or the ball is coupled to the stabilizingmember at another location. The vibration damping includes a housing4212, a trigger extension member 4214, and a biasing member 4216, suchas a spring or other resilient member. The housing 4212 is disposed onthe end of the rod 4008. In the embodiment illustrated by FIG. 42, theball 4030 is defined as part of the housing 4212. In the embodimentillustrated by FIG. 43, the housing 4212 does not include a ballportion. The trigger extension member 4214 is disposed in the housing4212 in engagement with the control rod 4210. The biasing member 4216biases the trigger extension member 4214 against the button 4006. Thebiasing member 4216 applies a preload to the button 4006 to inhibitvibration of the button 4006 in the rod 4008. The force applied by thebiasing member 4216 is small enough that the biasing member 4216 doesnot depress the control rod 4210 to a point where the stabilizing member3214 a, 3214 changes state (i.e. from an engaged state to a disengagedstate).

Referring to FIGS. 36 and 37, each rear caster pivot arm 3220 a, 3220 bis independently coupled to the frame 3202 at a pivotal connection 3602a, 3602 b. Each rear caster 3210 a, 3210 b is coupled to a rear casterpivot arm 3220 a, 3220 b, such that each rear caster can rotate around asubstantially vertical axis. FIGS. 44-50 illustrates the rear casterposition sensing arrangement 4400 and a rear caster suspension 4402 ofthe wheelchair 3200. The rear caster suspension 4402 includes the rearcaster pivot arms 3220 a, 3220 b, the rear casters 3210 a, 3210 b, andbiasing members 4408 a, 4408 b, such as a spring or other resilientmember. A stop member 4413 a, 4413 b is attached to each pivot arm. Thestop members 4413 a, 4413 b rotate with the pivot arms 3220 a, 3220 b.The rear caster position sensing arrangement 4400 includes a pair ofspaced apart trigger engagement assemblies 4420 a, 4420 b that arecoupled to the wheelchair frame at pivotal connections 4422 a, 4422 b.In the illustrated embodiment, each rear caster position sensingarrangement includes an elongated member 4423 pivotally coupled to theframe, and an adjustable trigger engagement member 4425 connected to theelongated member 4423.

The adjustment between the engagement member 4425 and the elongatedmember 4423 allows the amount of rotation of the rear caster positionsensing arrangement that causes engagement of the stabilizing members tobe adjusted. Referring to FIGS. 45 and 46, the distance that theengagement members 4325 extend from the elongated members 4323 isadjustable. The distance that the engagement members 4325 extend fromthe elongated members determines the amount of rotation of the rearcaster position sensing arrangement that is required to cause thestabilizing assemblies to engage and disengage. In another embodiment,the trigger engagement assemblies 4420 a, 4420 b are replaced with thesingle piece trigger engagement members.

In the embodiment illustrated by FIGS. 44-50, the pivotal connections4422 a, 4422 b are coaxial with pivotal connections 3602 a, 3602 b ofthe rear caster pivot arms. In another embodiment, the pivotalconnections 4422 a, 4422 b are offset form the pivotal connections 3602a, 3602 b. The elongated members 4420 a, 4420 b are connected togetherby a bar 4424. Referring to FIGS. 45 and 51, the bar 4424 is disposedbetween first and second engagement surfaces 4430, 4432 of the stopmembers 4413 a, 4413 b. The bar 4424 selectively engages the stopmembers 4413 a, 4413 b to limit relative movement between the first andsecond rear caster pivot arms 3220 a, 3320 b. The biasing members 4408a, 4408 b are interposed between the rear caster pivot arms 3220 a, 3220b and the elongated members 4420 a, 4420 b.

The rear caster position sensing arrangement 4400 operates to cause bothsensors or triggers to place both of the stabilizing members 3214 a,3214 b in the engaged and disengaged states based on the positions ofthe rear caster pivot arms 3320 a, 3320 b. FIG. 49 illustrates rearcaster pivot arm 3320 a in a normal operating position. Rear casterpivot arm 3320 b is not visible in FIG. 49, because it is in the same,normal operating position, as rear caster pivot arm 3320 a. When (shownschematically in FIG. 49) one or both of the rear caster pivot arms 3320a, 3320 b are in normal operating positions relative to the frame 3202,one or more of the biasing members 4408 a, 4408 b hold both of thetrigger engagement assemblies 4420 a, 4420 b against both of the sensorsor triggers 3212 a, 3212 b, such that both stabilizing members aredisengaged. The elongated members 4420 a, 4420 b position the bar 4424with respect to the stop members 4413 a, 4413 b. As long as forceapplied by one or more of the biasing members 4408 a, 4408 b issufficient to maintain the elongated members 4420 a, 4420 b against thesensors or triggers 3212 a, 3212 b, the position of the bar 4424 isfixed. When there is a gap between the bar 4424 and a stop member 4413a, 4413 b, the rear caster pivot arms 3320 a, 3320 b are free to moveupwardly and downwardly with respect to one another.

In FIGS. 44 and 49, the stop members 4413 a, 4413 b are in contact withthe bar 24. When the stop members 4413 a, 4413 b engage the bar 4424,further relative movement of the of the rear caster pivot arms isinhibited by the bar 4424. In the position shown by FIGS. 44 and 49, thebar 4424 is in engagement with the engagement surface 4430 of both ofthe stop members. As a result, downward movement of only one pivot arm3320 a, 3320 b (with the other pivot arm remains in the positionillustrated by FIGS. 44 and 49) is inhibited by the bar 4024 and thebiasing member 4408 a or 4408 b of the other pivot arm. However, bothpivot arms 3320 a, 3320 b can pivot downward together relative to theframe. Referring to FIG. 49A, downward movement indicated by arrow 4902of both pivot arms 3220 a (3220 b is hidden) allows the rear casterposition sensing arrangement 4400 to move away from both of the triggers3212 a, 3212 b, allows the triggers to extend, and causes both of thelocking members 3214 to disengage. As such, the rear caster pivot arms3320 a, 3320 b move independently from the position shown in FIG. 49 inthe direction of arrow 4904. Movement of each rear caster pivot arms3320 a, 3320 b from the position shown in FIG. 49 in the directionindicated by arrow 4902 is dependent on the other rear caster pivot armalso moving in the direction indicated by arrow 4902.

Referring to FIG. 41, each stabilizing member 3214 a (3214 b not shown)is coupled to the frame 3202 and the front caster pivot arms 3218 a,3218 b. The stabilizing members 3214 a (3214 b not shown) allow upwardand downward movement of the first and second front caster pivot arms3218 a, 3218 b relative to the frame 3202 when first and second rearcasters 3210 a, 3210 b are each in a normal position relative to theframe shown in FIG. 41, because the rear caster position sensingarrangement 4400 engages both of the triggers 3212 a, 3212 b of thestabilizing members 3214 a, 3214 b in this position.

When the wheelchair 3200 exhibits a tipping behavior, the frame 3202 ofthe wheelchair is pitched slightly forward toward the front casters 3208a, 3208 b. As a result, both of the rear casters 3320 a, 3320 b movedownward relative to the frame 3202 to maintain contact with the ground.This downward movement moves the rear caster position sensingarrangement 4400 away from the triggers 3212 a, 3212 b, allows thetriggers to move to the extended position and causes the stabilizingassemblies 3214 a, 3214 b to engage. In an exemplary embodiment, thestabilizing assemblies 3214 a, 3214 b engage to lock the first andsecond front casters 3208 a, 3208 b against upward movement relative tothe frame, but allow the front casters to move downward when engaged.The stabilizing assemblies 3214 a, 3214 b may be configured in anymanner that inhibits further tipping of the wheelchair frame when thestabilizing members are engaged. In another embodiment, the stabilizingassemblies 3214 a, 3214 b lock the front caster pivot arms against bothupward and downward movement with respect to the pivot arm when engaged.When one or more of the rear casters return to a normal operatingposition relative to the frame, the triggers are depressed again todisengage and allow upward and downward movement of the front castersrelative to the frame. In the wheelchair 3200, the rear caster positionsensing arrangement is configured such that movement of one of the rearcasters to a normal operating position moves the other rear caster up aswell.

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. For example, pivotal connections can be madeof any number of structures including bearing assemblies, pins, nuts andbolts, and frictionless sleeve assemblies. Additionally, springs orshock absorbers can be added between pivoting and non-pivotingcomponents to limit, dampen, or somewhat resist the pivotal motions ofthese components. Also, a brake-disc locking mechanism could beintegrated into any of the pivotal connections and serve as astabilizing member or assembly that locks components coupled to thepivotal connection from rotation when actuated and freely allows pivotalmotion about the connection when not actuated. Therefore, the invention,in its broader aspects, is not limited to the specific details, therepresentative apparatus, and illustrative examples shown and described.Accordingly, departures can be made from such details without departingfrom the spirit or scope of the applicant's general inventive concept.

What is claimed:
 1. A wheelchair comprising: a frame; a pair of drivewheels supporting the frame; a first front caster coupled to the framesuch that the first front caster is moveable upwardly and downwardlywith respect to the frame; a second front caster coupled to the framesuch that the second front caster is moveable upwardly and downwardlywith respect to the frame; a first rear caster coupled to the frame suchthat the first rear caster is moveable upwardly and downwardly withrespect to the frame; a second rear caster coupled to the frame suchthat the second rear caster is moveable upwardly and downwardly withrespect to the frame; at least one stabilizing assembly coupled to thefirst and second front casters; a trigger that disengages thestabilizing assembly when in a first state and engages the stabilizingassembly when in a second state; a rear caster position sensorsarrangement disposed between the trigger and the first and second rearcasters such that at least one of the rear casters force the triggeractuating arrangement to place the trigger in the second state todisengage the stabilizing assembly when at least one of the rear castersare in a normal operating position, and such that the rear casters causethe trigger actuating arrangement to place the trigger in the firststate to engage the stabilizing assembly when both of the rear castersmove downward from normal operating positions relative to the frame. 2.The wheelchair of claim 1 wherein the rear caster position sensingarrangement presses against the trigger to place the trigger in thefirst state.
 3. The wheelchair of claim 1 wherein the rear casterposition sensing arrangement is coupled to the rear casters by one ormore springs.
 4. The wheelchair of claim 1 wherein the rear casterposition sensing arrangement is pivotally connected to the frame.
 5. Thewheelchair of claim 1 wherein the rear caster position sensingarrangement limits downward movement of the first caster with respect tothe second caster.
 6. A wheelchair comprising: a frame; a seat supportedby the frame; a pair of drive wheels supporting the frame; a first frontcaster coupled to the frame such that the first front caster is moveableupwardly and downwardly with respect to the frame; a second front castercoupled to the frame such that the second front caster is moveableupwardly and downwardly with respect to the frame; a first rear castercoupled to the frame such that the first rear caster is moveableupwardly and downwardly with respect to the frame; a second rear castercoupled to the frame such that the second rear caster is moveableupwardly and downwardly with respect to the frame; a stabilizing meansfor selectively inhibiting upward movement of the first and second frontcasters relative to the frame; wherein the stabilizing means is in adisengaged state and allows upward and downward movement of the firstfront caster and the second front caster relative to the frame when thefirst rear caster moves downward from a normal operating positionrelative to the frame and the second rear caster is in a normaloperating position relative to the frame; and wherein the stabilizingmeans inhibits upward movement of the first front caster and the secondfront caster relative to the frame when both of the rear casters movedownward from normal operating positions relative to the frame.
 7. Awheelchair comprising: a frame; a pair of drive wheels supporting theframe; a first front caster coupled to the frame such that the firstfront caster is moveable upwardly and downwardly with respect to theframe; a second front caster coupled to the frame such that the secondfront caster is moveable upwardly and downwardly with respect to theframe; a first rear caster coupled to the frame such that the first rearcaster is moveable upwardly and downwardly with respect to the frame; asecond rear caster coupled to the frame such that the second rear casteris moveable upwardly and downwardly with respect to the frame; astabilizing means for selectively inhibiting upward movement of thefirst and second front casters relative to the frame; wherein thestabilizing means inhibits upward movement of the first front caster andthe second front caster relative to the frame when both of the rearcasters move downward from normal operating positions relative to theframe; and wherein the stabilizing means allows upward movement of thefirst and second front casters relative to the frame when one or more ofthe rear casters return to a normal operating position relative to theframe.